To narrow down the topic "The Economic History of the United States," the two correct choices would be:
-
Economy of the Southern Colonies in America 1600-1775 - This choice focuses specifically on the economic aspects of a defined region and time period within U.S. history.
-
The New England Mill Economy in the United States in the 1800s - This choice also focuses on a specific aspect of economic history in a particular region and time frame in the U.S.
These selections focus directly on economic topics within the U.S., making them appropriate for narrowing down the broader topic.